This proposal is designed to define the critical regulatory events that moderate the development of a simple haploid eukaryote, the slime mold Dictyostelium discoideum. Previous experiments have shown that during the development of Dictyostelium, the major change in the transcription pattern occurs at a very discrete stage when it changes from unicellular to multicellular form. Specific cell-cell interaction induces the synthesis and maintains the stability of 2500 mRNA sequences that are not found in the single cell stage. As a first step toward understanding the mechanism of this developmental regulation, the structure of several genes whose expression is regulated by cell-cell interaction will be analyzed. Several Dictyostelium DNA gragments containing such genes have been cloned in bacteriophage lambda. The coding regions of these genes will be mapped and their transcriptional start sites and termination sites will be located. Regions of the gene that promote or regulate the transcription of these genes will be determined by in vitro transcription or transformation, and their chromatin conformation during transcribed and non-transcribed conditions will be probed with DNase I. These will form the basis for further understanding the mechanism of transcriptional control and the role of cell-cell interaction in the regulation of development.